Method For The Alloying Of Aluminum To Form Components

ABSTRACT

To achieve the object of providing a method by which the disadvantages entailed in the production of components made from materials that contain aluminum are avoided, a method for alloying aluminum to form components is described, the alloying of aluminum taking place by adding an aluminum-containing material, the component being surrounded by at least one means for receiving aluminum-containing material and the element that is formed in such a way being sintered. Preferably, the component is surrounded in at least one metal nonwoven material, aluminum foil being disposed between the nonwoven material and the component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No. PCT/EP2006/05938, filed Jun. 21, 2006, which claims the benefit of German Application No. 10 2005 033 073.8, filed Jul. 15, 2005

FIELD OF THE INVENTION

The present invention concerns methods for alloying aluminum to form components, as well as components produced using these methods.

BACKGROUND OF THE INVENTION

Because of its special properties, aluminum is a preferred material, in particular in the field of space and automotive engineering. Components made from aluminum and/or aluminum-containing materials are lighter compared with common components, e.g. components made from cast iron. Reducing weight in automobiles, for example, makes it possible to increase the efficiency rate as well as decrease fuel consumption and improve exhaust gas values. For example, in engines and transmissions, at this point in time, pieces that were formerly made from steel and cast iron are gradually being replaced by those made from aluminum and/or components produced by using aluminum. Since combining steel and/or cast iron parts with parts made from aluminum creates problems in terms of the different physical behaviors of the materials involved, it is desirable to replace as many conventional components made from steel or cast iron as possible by those manufactured by using aluminum. This avoids problems in terms of the differences of the materials used insofar as the thermal expansion coefficients, thermal conductivity, elastic properties, etc. are concerned. By using closely matching components manufactured by using aluminum, in particular, higher efficiency rates can also be attained.

Since many engine, clutch, and transmission components are manufactured by using powder metallurgical technology, there is a large interest in providing methods which permit the production of aluminum components by using powder metallurgical technology. However, the powder metallurgical manufacture of components by using aluminum is disadvantageous, in particular insofar as aluminum and its alloys tend to become coated with a very stabile metal oxide whenever they come into contact with air. In particular, the specific surface is increased as a result thereof. The oxide layers that are located on the aluminum-containing material that is used hinders the diffusion of the particles of the powder material that is used, which is necessary for sintering. In addition, components that are made from aluminum-containing materials exhibit reduced strength values compared with components made from steel or cast iron, in particular lower hardness. Additionally, the oxide layers that are located on the aluminum-containing initial material inhibit cold bonding among the particles during the usual compression molding.

For example, steel with the German material number 1.4767 is a typical aluminum-containing steel. When using such aluminum-containing steels, however, it is particularly disadvantageous that they perform poorly during the sintering step due to the high oxygen affinity of the aluminum already described above. In addition, water atomization of such aluminum-containing steels is not acceptable from an economical point of view. In case such aluminum-containing steels are intended to be used as fibers and, consequently, actual sintering is planned to be preceded by a wire-drawing step, the metal oxide layer also causes significant tear of the drawing die used.

As a result, there is a need for a method by means of which aluminum-containing components are manufactured while simultaneously, during the manufacture, the known disadvantages of state-of-the-art methods are avoided. The object of the present invention is therefore to provide a method for alloying aluminum to form such components which avoids the aforementioned disadvantages.

SUMMARY OF THE INVENTION

The present invention is directed to methods for making alloyed-aluminum components, the methods comprising providing at least one aluminum-containing material; providing a component to be alloyed with aluminum; surrounding the component with at least one means for receiving the at least one aluminum-containing material; and sintering the resulting element. The present invention is further directed to components produced in accordance with the described methods.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In accordance with the present invention, the object is achieved by a method for alloying aluminum to form components wherein the alloying of aluminum is carried out by adding an aluminum-containing material, wherein a component is surrounded by a means for receiving at least one aluminum-containing material, and the resulting element is sintered. For the purposes of the present invention, insofar as the method in accordance with the present invention is concerned, the term “sintering” particularly refers to achieving a sufficient temperature at which aluminum is transferred to the gaseous phase and, as a result, at least partially, precipitates on the surface of the component in question and, subsequently, in case sufficient temperatures are present, diffuses into the material of the component. As a result, by using the method in accordance with the present invention, in particular, components are obtained which, in a surface-near layer, have a higher content of aluminum. Needless to say, carrying out the method in accordance with the present invention requires that the component to be provided with aluminum does not itself liquefy at the temperatures that are required for the diffusion of the aluminum into the component. The component to be provided with aluminum itself may contain aluminum (a low content of aluminum, in particular with an aluminum content of less than 2 of percent by weight), although preferably, such component is essentially aluminum-free. One advantage over the incorporation of powder/fibers, provided such powder/fibers are/would be available, is that there are no changes in material consistency in terms of pores, which are caused by melting of the aluminum.

The method in accordance with the present invention is particularly advantageous insofar as, for example, based on common iron-chromium steels, which optionally contain other metals, in particular rare earths, first, components including green compacts with high resistance values can be produced which, during another step and in respect of their properties, can be manipulated in particular in the surface-near areas by alloying aluminum and whose aluminum content can be specifically set.

The aluminum-containing material, which, for example, is an aluminum alloy, preferably pure aluminum, liquefies during the sintering step once it reaches the melting temperature, which, for example in the case of pure aluminum, has a value of approx. 660° C., wherein the aluminum-containing material, which is liquid at that temperature, is diffused throughout the means receiving the aluminum-containing material. As a result, dropping of the aluminum-containing molten material is reduced, and the concentration of aluminum in immediate proximity of the component to be provided with aluminum is maintained at a high level as a result thereof. When dropping below the vapor pressure, preferably above approx. 1000° C., of the aluminum-containing molten material, aluminum becomes gaseous and is enriched in the vapor. Since the aluminum-containing vapor develops in immediate proximity of the component to be provided with aluminum, the gaseous aluminum may at least partly precipitate on the surface of the respective component and, once the sintering temperature of the component is reached, will diffuse into the surface-near layers of the same. The dissolved aluminum exhibits a thermodynamically lower vapor pressure and remains stable in the component. As a result, the method in accordance with the present invention is characterized by a total of at least three temperature levels during the sintering step, wherein at the first temperature level, the aluminum-containing material liquefies, the second temperature level characterizes the vaporization of the aluminum, and at the third temperature level, actual sintering and diffusion of the aluminum into at least the surface-near areas of the component takes place.

The means for receiving the aluminum-containing material preferably has a sufficiently large, in particular high pore volume and has preferably a non-woven structure, wherein in a particularly preferable manner, a non-woven material made from metal and/or ceramic is used. Preferably and as a basic rule, the means for receiving the aluminum-containing material should have a large surface, as a result of which the aluminum and/or aluminum-containing material which has melted after reaching the first temperature level is absorbed in a uniform manner and over a large surface and, as a result thereof, it is also uniformly distributed throughout the component surrounded by the means receiving the aluminum-containing material. As a result, if desired, a very uniform diffusion of the aluminum in the entire surface-near layer of the component can be achieved.

The sintering step of the method in accordance with the present invention is preferably carried out above the vaporization temperature of the aluminum-containing material, as already addressed above. The temperature at which the aluminum is alloyed through diffusion into the surface-near layers of the component is preferably at least 1000° C. The vaporization temperature of the aluminum and/or of the aluminum-containing material may be lower.

In a preferred embodiment in accordance with the present invention, the component is selected from a group comprising sintered and/or unsintered parts, in particular compacts, non-woven materials, powder muck or fiber mats. The method in accordance with the present invention can therefore be applied for yet unsintered components as well as already sintered components. For example, compacted green compacts may be surrounded, prior to sintering in accordance with the method in accordance with the present invention, with the means for receiving the aluminum-containing material and be sintered while adding the aluminum-containing material, wherein at the same time as sintering, the aluminum is also alloyed. Sintering of the component and alloying of aluminum, however, can also be performed in separate steps.

The aluminum-containing material is preferably used in the form of a metal foil, as a powder, as a wire, as a woven material, and/or as a fiber. The use in the form of an aluminum foil which, additionally, is embossed on at least one side to increase the surface and simplify the transfer of the aluminum into the vapor phase is particularly preferred. Preferably, the aluminum-containing material is made from pure aluminum.

The aluminum-containing material, however, may also be made from aluminum-containing alloys. These alloys may, for example, be manufactured from powder mixtures comprising between 60 and 98.5 percent by weight, based on the total quantity of the powder mixture, preferably between 75 and 92 percent by weight, of an aluminum base powder from metals and/or their alloys, comprising aluminum, between 0.2 and 30 percent by weight of magnesium, between 0.2 and 40 percent by weight of silicon, between 0.2 and 15 percent by weight of copper, between 0.2 and 15 percent by weight of zinc, between 0.2 and 15 percent by weight of titanium, between 0.2 and 10 percent by weight of tin, between 0.2 and 5 percent by weight of manganese, between 0.2 and 10 percent by weight of nickel and/or less than 1 percent by weight of arsenic, antimony, cobalt, beryllium, lead and/or boron, wherein all percentages by weight are based on the total quantity of an aluminum base powder. In addition, into the powder mixture for the manufacture of an aluminum-containing alloy, additionally or alternatively, between 0.8 and 40 percent by weight, preferably between 7 and 15 percent by weight, based on the total quantity of the powder mixture, of a metal powder selected from a group of metals and/or their alloys comprising iron, molybdenum, wolframium (tungsten), chromium, vanadium, zirconium and/or yttrium, can be incorporated.

In an alternative embodiment in accordance with the present invention, first, the aluminum-containing material is brought into contact with the component and, subsequently, the component is surrounded with the means for receiving at least one aluminum-containing material. For the purposes of the present invention, “bringing into contact” not only refers to any direct contact between the aluminum-containing material and the component, but also to partial contact and/or contact with a part of the surface as well as the arrangement of the aluminum-containing material close to and/or immediately adjacent to the component.

In another alternative embodiment in accordance with the present invention, first, the aluminum-containing material is placed on the means for receiving the aluminum-containing material and, subsequently, the material is brought into contact with the component by surrounding the same with the means. In another alternative embodiment, it is also possible that, after surrounding the component with the means for receiving the aluminum-containing material, the aluminum-containing material is used in the area between the component and the means. Such an alternative embodiment is particularly suited in case aluminum-containing material is used as a powder and/or fiber and/or their mixtures.

In another preferred embodiment in accordance with the present invention, the component is surrounded by at least one metallic non-woven material, wherein between the non-woven material and the component, an aluminum foil is arranged, in particular also an embossed aluminum foil. This preferred embodiment is particularly advantageous insofar as it makes it possible to dispose a relatively high quantity of aluminum in a simple and safe manner in immediate proximity of the component, and insofar as the resulting wrapping is easy to handle during the subsequent sintering step and/or alloying step. In addition, by using a foil, the concentration of aluminum during the vapor phase can be uniformly set throughout the entire area surrounding the component. It is also possible that either a single-layer or multilayer aluminum foil is used, or several foil layers are used individually on top of each other. Conventional embossed and non-embossed aluminum foils, also known from the packaging industry, are used.

In case a green compact is used in accordance with the present invention, such green compact may also be subject to subsequent compression (which may also be called intermediate compression). For example, a compacted green compact may once again be placed in a common matrix mold where it can at least partly be subsequently compressed by using the respective plungers. Preferably, the tools used for subsequent compression may entirely or partly have a conical design, as a result of which, in certain predefined parts of the green compact, particularly high compressions can be achieved. Prior to the alloying of aluminum and/or prior to sintering of the green compact, the green compact is preferably dewaxed. Dewaxing is preferably carried out under nitrogen, oxygen, air and/or mixtures of the aforementioned gases, in particular also with the specific supply of air. In addition, dewaxing may involve endogas and/or exogas, in this case preferably in vacuum. Preferably, dewaxing may use microwaves and/or ultrasound or only microwaves for temperature control. Finally, dewaxing may also be achieved by using solvents such as alcohol or the like or critical carbon dioxide with or without the use of temperature, microwaves or ultrasound or via a combination of the aforementioned methods.

After the step of alloying the aluminum, the actual sintering step can be carried out. In case the component is already a sintered component or a massive component, afterwards, a necessary heat treatment, in particular homogenization annealing, may be optionally performed. Heat treatment can be conducted depending on the chemical composition of the resulting component. Alternatively or in addition to heat treatment, the sintered component may also be quenched—based on the sintering and/or homogenization annealing temperature—preferably in water or via gas quenching.

Prior to or after sintering or alloying of the aluminum, additional surface densification, or more generally: the application of internal compression stresses in superficial areas, in particular by means of sandblasting or shot peening, rolling or the like, may be carried out. Also, prior to or after homogenization annealing, calibration may be carried out. Calibration is performed at room temperature or at an elevated temperature up to the forging temperature, also with the use of pressure of up to 900 N/mm². Optionally, calibration can even be carried out above the solidus line, in which case the component can also be removed directly at the sintering heat and/or at the temperature used for alloying the aluminum.

The present invention furthermore concerns a component manufactured in accordance with the method in accordance with the present invention. A component manufactured in accordance with the present invention is particularly characterized in that, in the surface-near areas, an increased aluminum content can be detected. The resulting component may at least partly have a higher aluminum content in such areas.

The components that are produced by using the method in accordance with the present invention may be used in particular for hot gas filtering, but also in particular for waste gas filtering for combustion engines, and in this case in particular as carriers for catalytic converters or as a soot filter. In addition, the components produced by using the method in accordance with the present invention may be used in membrane reactors in which gas reactions take place.

Nonetheless, they can also be used as other substrates for non-metallic layers. As a basic rule, the components manufactured by using the method in accordance with the present invention display an increased oxidation resistance compared with components without any increased aluminum content in the surface-near layer.

These and further embodiment shall be illustrated in more detail in the following examples:

Example 1

From an Inconel 600 (nickel-chromium alloy) powder with the German material number 2.4816 (aluminum-free), a green compact was produced in the form of a tube. The powder mixture was isostatically compressed into a tube-shaped green compact at room temperature. The density of the green compact was approx. between 2.35 and approx. 2.38 g/cm³. Afterwards, the green compact produced in such a manner was dewaxed for approx. 30 minutes at approx. 430° C.

Afterwards, the green compact produced in such a manner was wrapped in a single layer of common commercial aluminum foil, embossed on at least one side, and care was taken to ensure that the aluminum foil was in uniform and close contact with the tubular green compact. Such aluminum foil-wrapped component was subsequently placed between two metallic non-woven materials with a composition of 75% of iron, 20% of chromium, and 5% of aluminum, with these metallic non-woven materials having a porosity of 85%.

The resulting wrap was placed in a vacuum furnace. Once the temperature reaches the melting temperature of aluminum at approx. 660° C., the aluminum foil begins to melt, and the liquid aluminum is received by the two metallic non-woven materials in a uniform manner and over a large surface. This prevents dropping of the molten aluminum and, consequently, a reduction in the quantity of aluminum in the immediate proximity of the component. In case the vaporization temperature for aluminum is exceeded, the aluminum evaporates and precipitates over a large surface of the green compact made from aluminum-free steel that was used. As a result of subsequent or simultaneous sintering of the green compact at a temperature of approx. 1100° C. itself, the aluminum diffuses in the surface-near areas of the green pump impeller compact. The temperature in the furnace can be gradually increased, although it is also possible to immediately set a temperature above the vaporization temperature and, as long as this is desired, also above the sintering temperature at the same time.

Example 2

In another example, a fiber mat was sintered from the material with the German material number 1.4113 (aluminum-free) under the usual conditions. Afterwards, the sintered fiber mat was uniformly wrapped on both sides with aluminum foil, and the aluminum foil-wrapped fiber mat was subsequently placed between two metallic non-woven materials with a lower porosity and a larger surface than the fiber mat produced. Afterwards, aluminum was alloyed as already described above for the green pump impeller compact. As a result, a fiber mat was obtained with an alloyed aluminum content of more than 5 percent by weight, based on the total quantity of the fiber mat. For example, in the case of fiber mats made from the material with the German material number 1.4404 (aluminum-free), after alloying of aluminum under comparable conditions, the aluminum content of the finished fiber mat exceeded 1 percent by weight, based on the total quantity of the fiber mat. For example, after manufacturing a green compact from Inconel 600 powder, the aluminum content of the finished sintered component, after alloying in accordance with the above-described method by using an aluminum foil, exceeded 1 percent by weight, based on the total quantity of the component, which matches that of Inconel 601.

The present invention therefore provides a simple method which makes it possible, in particular, to provide aluminum-free materials with aluminum at least in the surface-near areas even after the manufacture of sintered components and therefore ensure the advantageous properties of the same. 

1. A method for making an alloyed-aluminum component, comprising providing at least one aluminum-containing material; providing a component to be alloyed with aluminum; surrounding the component with at least one means for receiving the at least one aluminum-containing material; and sintering the resulting element.
 2. The method in accordance with claim 1, wherein the means for receiving the aluminum-containing material is a non-woven material.
 3. The method in accordance with claim 1, wherein the means for receiving the aluminum-containing material is a non-woven material made from metal, ceramic, or a combination thereof.
 4. The method in accordance with claim 1, wherein the sintering step is carried out above the vaporization temperature of the aluminum-containing material.
 5. The method in accordance with claim 1, wherein the sintering temperature is at least 1000° C.
 6. The method in accordance with claim 1, wherein said provided component is sintered or unsintered.
 7. The method of claim 6, wherein the provided component is a powder compact, a non-woven material, fiber mat, or powder muck.
 8. The method in accordance with claim 1, wherein the provided component is aluminum-free or has a low content of aluminum.
 9. The method in accordance with claim 1, wherein the aluminum-containing material is in the form of a metal foil, a powder, wire, woven material, or a fiber.
 10. The method in accordance with claim 1, wherein the aluminum-containing material is made from essentially pure aluminum.
 11. The method in accordance with claim 1, wherein the aluminum-containing material is first brought into contact with the component and, subsequently, the component is surrounded with the means for receiving the at least one aluminum-containing material.
 12. The method in accordance with claim 1, wherein the aluminum-containing material is first placed on the means for receiving the aluminum-containing material and, subsequently, the material is brought into contact with the component by wrapping the component with the means for receiving the aluminum-containing material.
 13. The method in accordance with claim 1, wherein the aluminum-containing material is arranged between the component and the means for receiving the aluminum-containing material.
 14. The method in accordance with claim 1, wherein the aluminum-containing material is aluminum foil and the means for receiving the aluminum-containing material comprises at least one metallic non-woven material and wherein the component is surrounded with the at least one metallic non-woven material and the aluminum foil is between the non-woven material and the component.
 15. An aluminum-alloyed component produced in accordance with the method of claim
 1. 